Mr Sharon's Likud party will decide in a crucial referendum of its members next Sunday whether to back his plan.

But yesterday it emerged that Benjamin Netanyahu, the finance minister and former prime minister; Silvan Shalom, the foreign minister, and Limor Livnat, the education minister, told Mr Sharon at the weekend that they would not campaign in public on his behalf, apparently because of concerns that the poll might be defeated.

Their decision not to risk their political futures by being closely associated with an initiative that has proved deeply unpopular with the Israeli Right came just a week after they had promised the prime minister their support.

They appeared to have pledged that they would help to deliver a Yes vote from hardliners in the Likud party in exchange for concessions over details of the plan, under which Jewish settlements and soldiers in the Gaza Strip would be withdrawn and four isolated settlements in the West Bank dismantled.

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Mr Sharon has staked his prestige and his future on the plan. His closest confidant, his son Omri Sharon, who is also a Likud MP, has warned party members that a defeat could cause his father to resign.

The wave of support for the plan that appeared to swell after President George W Bush gave it his blessing this month appears to have subsided and analysts predict that Mr Sharon could face defeat in the poll.

Recent opinion polls have indicated mounting reluctance among the Likud party rank-and-file to part with the Gaza settlements.

Mr Sharon is ahead in the polls but research indicates that his support is faltering among those party members who are most likely to turn out to vote.